1. Field of the Invention
The present invention relates to a circuit arrangement for determining specific characters occurring in a sequence of characters comprising at least one established sequence of character elements in a likewise established frequency, and for the emission of a message signal which can be used to trigger control processes only in the event that characters comprising an established sequence of character elements in a likewise established frequency have occurred directly consecutively in the sequence of characters, and more particularly for such circuits which are useful in teleprinter exchange systems.
2. Description of the Prior Art
A circuit arrangement of the type briefly described above, which is also referred to as a character sequence or symbol sequence recognition device, is already known in the art, for example from the U.S. Pat. No. 3,243,775. However, with the aid of this known circuit arrangement it is only possible to determine a specific sequence of binary digit signals from a number of consecutively occurring binary digit signals. Since a magnetic core storage arrangement is used in the known circuit arrangement to establish a character sequence or smybol sequence, it is not possible to modify the character sequence or symbol sequence which is to be taken into account in a simple manner.
A circuit arrangement is also known for establishing the existence of and analyzing teleprinter character sequences of a specific type and length for the purpose of further processing (treatment, guidance, further transmission or re-coding) of the teleprinter communications contained in the latter in telecommunications, in particular teleprinter exchange systems, such as found in the allowed German Application 11 47 970. In this known circuit arrangement, each of the teleprinter lines connected to a teleprinter exchange device is assigned its own intermediate memory having a storage capacity which is sufficient for one single teleprinter character. Also provided in an analysis device which is common to all the teleprinter lines connected to the relevant teleprinter exchange device and which can be connected by a connection device operated in time multiplex in time sequence to the individual intermediate memories assigned to the lines, and non-destructively reads out the teleprinter character stored in the memories and supplies the same to the analysis device. The analysis device contains a short-term memory for a number, which remains constant (for example 8) of teleprinter characters which are compared in a comparison device, having a given program, for identity with the latter. In the event of the identity of the teleprinter character sequence contained in the short-term memory with the given program, this comparison device will easily signal, whereupon the entire teleprinter character sequence is transferred, unchanged, into a data memory, whereas in the case of non-identity and the establishment of a new teleprinter character in the respective intermediate memory of the line, the teleprinter character which has been stored for the longest time is erased and replaced by the new teleprinter character at the end of the teleprinter character sequence following the last teleprinter character to have been input, and thus, the teleprinter character sequence is input into the data memory in modified form. Also in this known circuit arrangement, the directly consecutive occurrence of specific, in each case identical, teleprinter characters, is not used to trigger special message signals. Moreover, the above-considered known circuit arrangement involves a relatively high circuit expense which occurs, in particular, due to the special manner in which the analysis device is operated.
Finally, a circuit arrangement is also known for the evaluation and recognition of a specific character sequence, which consists of a given number of element-coded characters, which are identical to one another and each contain only a single polarity change, in telecommunication systems, in particular teleprinter exchange system, such as disclosed in German Patent 17 62 503. However, nothing is known in this connection regarding the evaluation and recognition of a specific character sequence which consists of a given number of identical characters of arbitrary form.